FREE WATER, PARTICULATES, AND CONTAMINANTS IN AVIATION FUELS: ASTM D6986
EXPLANATION
Fuel quality is paramount in aviation fuels because of their critical application. Many successive types of inspections are conducted to ensure quality protection. Rapid, visual inspections carried out at various locations in the fuel supply system are a critical part of the inspection program. Experience has shown that subjective evaluations such as described in this test method form an effective field alert system that is backed by other, more quantitative tests. This test method duplicates much of Test Method ASTM D4176, a test method applicable to all distillate fuels. However, the present test method also includes field methods applicable especially to aviation fuels.
This test method covers two procedures for establishing the presence of free water, solid particulate, and other contaminants in aviation gasoline and aviation turbine fuels. Procedure A uses transparent containers, while Procedure B uses opaque containers. Both procedures are rapid methods for contamination detection, and include ratings of haze appearance and particulate presence. Uncertain or marginal results by either of these procedures would normally result in testing by Test Methods such as ASTM D2276, ASTM D5452, or ASTM D3240 for quantitative determination of contaminants. Particulate determination in appearance tests is sensitive to sampling procedures. The presence of a small number of particles may indicate, for example, that the sample line was not flushed to provide a representative sample. The persistent presence of even a small number of particles, however, may be cause for further investigation depending on the situation.
Experience has shown that an experienced tester using a clear bottle can detect as little as 40 ppm of free, suspended water in the fuel. Thus, a fuel rated as "clear and bright" can still fail lower limits set by quantitative methods. A rater will also have difficulty resolving particles smaller than 40 μm. Smaller particles must be determined by other methods such as ASTM D2276, ASTM D5452, or other chemical tests. Experience has shown the visual appearance of fuel in a white porcelain bucket to be the most suitable method for the detection of dye contaminants or other unusual discoloration. In the U.S., the white porcelain bucket is used to detect the dye.
TEST SUMMARY
Procedure A covers transparent sample containers, including the open jar and the closed circuit sampler, while Procedure B uses opaque containers such as the white bucket. In the open jar procedure, 750 mL of fuel is placed into a clear 1 L container and visually examined. The jar is closed and the sample is swirled and examined for visual sediment and water at the bottom of the vortex. Additionally, fuel clarity may be rated by placing a standard bar chart behind the sample and comparing its visual appearance with the standard haze rating photographs. The presence or absence of free water and of particulates is reported.
In the closed circuit sample procedure, approximately 3500 mL of fuel is placed into the sampler and is examined for clarity and for visual sediment or water droplets on the bottom of the sampler. Additionally, fuel clarity may be rated by placing a standard bar chart behind the sample and comparing its visual appearance with the standard haze rating photographs. The presence or absence of free water and of particulates is reported.
In the white bucket procedure, fuel to a depth of approximately 15 cm is collected in a white porcelain coated or stainless steel bucket. The sample is examined for solids or sediment, or both, on the bottom of the bucket. Sample clarity can be checked by the appearance of a small, shiny coil on the bucket's bottom. If fuel is dry, the raised letters on the coil should be easily readable. The amount of sediment can be described by a letter category using a rating guide. In both procedures, the sample is inspected for color or other unusual appearance. Field inspection procedures are performed immediately after sampling at fuel handling temperature conditions.
TEST PRECISION
No precision to these procedures can be determined since they are not quantitative procedures. Nor can a justifiable statement can be made regarding the bias of this method because a fuel haze can be the result of a number of causes and a relationship with any single absolute quantitative measurement is not possible.
